Not wanting to use treats to train a puppy or dog always just makes we wanna shake my head..they are a primary motivator (dogs need food, water, air and sex to live and prosper in nature) and a highly effective way of rewarding a dog for performing a behaviour. Behaviours that are rewarded occur more frequently, once the behaviour is learned and proofed the food rewards can be put on a variable schedule and eventually phased out completely (though I don't do it personally, believe me, the amount of work Cracker and I do deserves a bit of a paycheque!)
The chances are that by using "force" (and even a gentle push is FORCE) to get a sit in a dog that has no previous relationship with you (and therefore no trust in you yet) has probably increased her discomfort with you rather than build confidence in you. The head down, turned away, slinking behaviour is fearful and insecure behaviour.
Everything she does at this point that is remotely acceptable (making eye contact with you, laying nearby, sniffing you) should be rewarded with a very tiny and very yummy tidbit. This is about her relating YOU with good things and for dogs food (especially high value food like hotdog slices or tiny bits of chicken) is a very good thing.
Some myths related to treats as rewards:
1/ my dog will never perform the behaviour without a treat or seeing the treat.
Truth: Properly trained, fading the lure, adding the cue and proofing the behaviour removes the need to continually show the food.
2/I am worried my dog will become fat.
Truth: the reward is supposed to be MINISCULE, smaller than the nail on your pinkie finger. For easy behaviours in low distraction environments you can even use part of her meal kibble to train, do the training before dinner when they are hungry and then feed the rest at dinner time.
3/He should perform the behaviour because he wants to please me.
Truth: Dogs are innocently selfish. They do WHAT WORKS for them, not what works for you. This is why you teach them that doing what YOU like earns them something that THEY like. It's a win win. The converse of this is if they are doing something ANYTHING then it works for them. If it's something you do not like you have to work out in your head what it is that is working for them, find a way to remove the intrinsic reward and to exchange the behaviour for something else in a rewarding way to the dog.
3/Food treats are bribing the dog.
Truth: Bullpucky. I don't work for free and neither does my dog. Luring incorrectly could be considered a bribe but that is the error of the trainer, not the fault of the reward.
4/I will have to use treats forever.
Truth: once a behaviour is learned and your dog matures and figures out that doing what you ask is rewarding you can switch up rewards to other things (providing the dog finds it rewarding, each one is different.) A schutzhund dog's reward is to bite the bumper, a hunting dog's reward is to flush and retrieve the bird, a scenthound's reward is to get a chance to follow a scent or tree a raccoon, the herding dog gets released to run the sheep...your dog's reward may be a game of tug, a throw of a ball, being let off leash, having the door open to the backyard or even a chance to train some more (hello border collies!).
I think you may find that this little dog has a lot to teach you about dog behaviour and about training methods. I know mine did.